The helicopter crashed between two commercial buildings in the 9100-block of Mason Avenue in Chatsworth. In addition to the three people who died at the scene, one person was taken to the hospital in unknown condition, the Los Angeles Fire Department said.
An LAFD spokesperson said one of the people killed was a pedestrian on the ground. It's unclear whether the other victims were aboard the helicopter.
Officials also said it was not immediately known how many people were aboard the helicopter.
Firefighters said the helicopter was fully engulfed in flames when they arrived.
The fire department said four vehicles and two storage containers were damaged by the fire.
The National Transportation Safety Board and the Federal Aviation Administration will investigate.
The crash occurred less than a mile from the scene of a large bus collision that left at least two people dead. Footage showed an SUV lodged into a Metro bus and people being treated nearby.
ABC News contributed to this report